Pinz Lab

Investigating mechanisms leading to lipotoxic cardiomyopathy.

The research focus of my laboratory is on mechanisms leading to lipotoxic cardiomyopathy. With the growing incidence of obesity, and the burden this puts on the health care system, it is important to understand the mechanisms by which certain fatty acids and their metabolites change signaling pathways in cardiomyocytes that cause a decline in contractile performance. In particular, we focus on highly organized membrane micro-domains called caveolae. Caveolae are small flask-like membrane invaginations that on the intracellular membrane leaflet are lined by caveolin proteins. In the heart caveolin-1 and -3 are expressed and are responsible for maintaining caveolae structure. Using different high fat diets we investigate how a change in the membrane lipid composition affects caveolin proteins and what consequences this has for cardiac contractile performance. We utilize in vivo imaging techniques such as echocardiography and magnetic resonance imaging to measure cardiac contractile performance in the live mouse. To determine ex vivo contractile performance we use the Langendorff mode. We have determined that the loss of cardiac caveolin-3 by high fat feeding is part of the mechanism for lipid-induced cardiac contractile dysfunction. The figure below shows the intracellular localization of the caveolin proteins in isolated adult mouse cardiomyocytes from mice fed different high fat diets; MCT control diet, which is a high fat control diet containing only triglycerides, and palmitate diet containing about 11% of palmitate.

Figure 1: Palmitate-induced loss of T-tubular caveolin-3 and decreased protein levels. Intracellular localization of caveolin-1 and -3 in isolated cardiomyocytes from mice fed standard lab chow, MCT control or palmitate diet for 12 weeks. Caveolin-1 and -3 co-localize to the plasma membrane and the T-tubule system in standard diet fed mice. In MCT control diet fed mice caveolin-1 does not localize to the plasma membrane or the T-tubule system and in ~50% of the analyzed cardiomyocytes caveolin-1 signal was detected in the nucleus. MCT control diet does not change the localization or the amount of caveolin-3. In palmitate diet fed mice caveolin-1 and -3 co-localize to smaller areas of the plasma membrane, but not to the T-tubule system. Caveolin-1 also localizes to the nucleus in 50% of the cardiomyocytes imaged. Caveolin-3 is essentially absent from the T-tubule system in palmitate diet fed mice. This figure demonstrates the lipid dependence of caveolin protein localization in cardiomyocytes.

Signaling and Caveolin

A separate part of our work focuses on signaling proteins and receptors that bind to the caveolin scaffolding domain (CSD domain) in caveolin-3. This includes the insulin receptor and endothelial nitric oxides synthase (eNOS). For both proteins we can demonstrate that the activity and localization depends on the presence of caveolin-3 at the plasma membrane. This work has implications for vascular disease and for diabetes, two of the most common co-morbidities of obesity.

Figure 2: Palmitate induces translocation of cellular eNOS in HL-1 cardiomyocytes concomitant with the loss of caveolin-3. Cells treated with control conditions show localization of eNOS around the cell periphery (first row), while treatment with palmitate (0.4 mM) causes movement to the cell’s interior (second row). In addition, cells were treated with an inhibitor of the de novo ceramide synthesis pathway, myriocin (5 µM), which can prevent eNOS translocation during palmitate exposure (two bottom rows). Green = eNOS, Red = lipid, Blue = DNA, Yellow = areas of eNOS/lipid colocalization.

In our future work, we want to investigate how the lipid-induced loss of caveolin proteins can be prevented and what a potential pharmacological treatment to replace caveolin-3 in the heart may entail.